USB charger voltage drop protection

I have ASUS Tinker Board, which is essentialy just a better version of Raspberry Pi 3. I am using relatively high-quality 5V 2A USB charger, as it was the most powerful I could find. ASUS says that 2A should be fine, even 1.7A as long as I don't plug in any power-hungry peripherals, which I won't do because I want it to run a headless server 24/7.
The problem here is that it does not have any voltage-drop, "micro-blackout" protection. And the charger, being intended for mobile phones with batteries in them, also lacks this feature.
The even larger problem is, that the Tinker Board, instead of CPU throtteling during voltage drop simply reboots itself, killing all processes running on it.
Is there a way I can protect this charger/board setup? I was thinking connecting a capacitor between T.Boards power pins, as they act as both power output and input. Would that work? Or is there some sort of device that can protect a single wall outlet from these micro voltage drops?

 

A capacitor is a reasonable solution to try, in fact you might try two: A big-ish electrolytic and a 0.1µF ceramic to catch any fast transients.

Notice that charging the cap will add to the start-up load on the power supply. That might be fine but it's common to use techniques to slow the inrush current and then switch out that protection once the cap is ready to go.